This invention relates to a solder for padding or filling operations on automobile bodies.
In the manufacture of automobile bodies, a repairing or smoothing operation is generally needed for filling in dents in the bodies and spaces in joints of sheet metal parts as a preparatory step to a surface coating operation. Commonly a lead-base alloy solder of the type known as filling solder, padding solder or body solder is used as the filling material in this smoothing operation. Filling solders currently in practical use for this operation contain a relatively large amount, for example, about 13-25 Wt%, of tin and a smaller amount of (for example, 2% or less) antimony.
A high percentage of tin in a lead-base filling solder affords the solder a good workability needed for the described use but inevitably renders the solder considerably expensive. Since the reduction of production costs is one of primary concerns of the present-day automobile industry, even the price of the filling solder is a matter of concern. Besides, the use of conventional filling solders offers a problem to the subsequent coating operation. In the surface coating operation, it is a current trend to use resin-base paints and varnishes which need a high temperature baking process for hardening. Sometimes the baking temperature is as high as 200.degree. C or even above. Then the above described conventional filling solders, applied to the automobile bodies, tend to locally soften or physically weaken and cause the appearance of defects such as blow-holes and traces of trickles on the coated surface.